here is a possible solution:

start the list

guests = []
guestAddition = input ('please enter guest name, enter stop when done')
while guestAddition != 'stop' :
guests.append(guestAddition)
guestAddition = input ('please enter guest name, stop to finish')
#print the list as entered
print (guests)
#sort the list
guests.sort()
#print the names one by one in alphabetical order
numValues = len (guests)
for steps in range(numValues) :
print (guests[steps])